Dietary overlap and optimal prey environments of larval and juvenile sardine and anchovy in the mixed water region of the western North Pacific

Studies on recruitment variability in Japanese sardine Sardinops melanostictus and Japanese anchovy Engraulis japonicus have focused on the mixed water region (MWR) and its southern waters in the western North Pacific. However, the availability of suitable prey for larval and juvenile sardines and anchovy in the MWR was poorly known. Here, we describe the feeding habits and prey environments of larval and juvenile Japanese sardine and Japanese anchovy in the MWR from 1970-2013, during a time of dramatic changes in sardine and anchovy stocks. Fish and zooplankton were sampled from April to July using a variety of nets. Larval and juvenile sardine and anchovy fed on similar prey, such as copepodites of calanoid (e.g. Paracalanus spp.) and poecilostomatoid (e.g. Corycaeus affinis and Oncaea spp.) copepods, except for between 1988 and 1991. The abundance of dominant copepod prey species varied with sea surface temperature, with P. parvus and C. affinis most abundant at approximately 16 to 17 degrees C and Oncaea spp. at temperatures exceeding 20 degrees C. Decreased abundance of P. parvus after 1988 coincided with poor sardine recruitment. Although larval and juvenile sardine and anchovy have similar diets in the MWR, temperature possibly affects the distribution and abundance of their prey, and consequently fish stocks in the Kuroshio-Oyashio ecosystem.